1. Field of the Invention
The present invention relates to electrical connecting boxes suitable for installation in locations such as engine rooms of vehicles, where temperature varies from high to low, and further relates to methods for protecting printed circuit boards and mounted parts thereon.
2. Description of the Related Art
In recent years, accompanying the rise in the need for vehicles to have various amenities, there has been a tendency for an increasing number of electrical components to be mounted in vehicles. Or more concretely, a variety of electrical components have become mountable onboard vehicles, including for example, audio systems, navigation systems, televisions, powered antennas, air conditioners, rear-window heaters, seat heaters, power seats, and suspension hardness control devices (as an example, refer to Japanese Patent Application Laid-Open Publication No. 2001-266997).
Power supply to these electrical vehicle components is conducted via an electrical connecting box installed in the vicinity of the battery inside the engine room. Furthermore, various electrical and electronic component parts such as fuses, relays are mounted in the electrical connecting box. The fuse prevents the outbreak of fire in the vehicle in the event of a short circuit between a wire harness and a body, as well as load failure of motor and the like. The relays control power supply to the vehicle's electrical components in conjunction with an operation of switch etc. in the vicinity of the driver's seat.
Generally, connections between the wire harness and the electrical connecting box are realized by means of connector connections.
FIG. 3 is an example of an electrical connecting box according to the related art of the present invention.
The electrical connecting box 5 has a configuration such that the printed circuit board is housed sandwiched in an enclosure comprised of an upper case 500 and a lower case 600. In the electrical connecting box 5, the above-described electrical and electronic parts are collectively mounted upon a printed circuit board. A mounted part 353 is mounted upon the surface of the printed circuit board 300 facing the upper case 500. A lead terminal 351 of an electronic part 350 extends via a through hole formed in the printed circuit board 300. Upon the lead terminal 351, for example, soldered portion 352 fixing the lead terminal 351 to the printed circuit board 300 are formed.
Since the upper case 500 and the lower case 600 are generally chosen to be composed of resin from an ease-of-molding and cost perspectives, it becomes easier situation for certain undesirable phenomena to occur after the cases 500 and 600 have been assembled as the electrical connecting box. The phenomena is physical interference between the upper case 500 or the lower case 600 and the lead terminal 351 or the soldered portion 352 upon the printed circuit board 300, or between the mounted part 353 like electrical or electronic parts and the upper case 500. Such interference derives from the introduction of unexpected variations in the dimensions of the cases 500 and 600 when they are shaped or are deformed afterwards by thermal effect of heat from the engine or external temperature.
For these reasons, in order to avoid impairing the functionality of the printed circuit board as a result of this kind of interference, generally, there is provided a considerably large clearance X between for example the upper case 500 and those parts upon the printed circuit board 300, as shown in FIG. 3. This clearance X is configured such that even if the upper case 500 undergoes bending, it will not adversely impact the functionality of the printed circuit board.
However, when this considerably large clearance is provided, the electrical connecting box itself becomes larger in dimension. And since the engine rooms of vehicles in recent years now house various other parts besides the engine, demand has risen for the size of the electrical connecting box itself to be made as small as possible.